The invention relates to a low-pressure mercury vapour discharge lamp comprising a discharge vessel which is sealed in a gastight manner and encloses a discharge space which contains a filling of mercury and a rare gas, which discharge lamp furthermore comprises means for maintaining an electric discharge in the discharge space, while a portion of the surface of the discharge vessel facing the discharge space has a reflector layer of aluminium oxide particles.
Such a lamp, which can be used for reprographic purposes, is known from EP 0,270,866. The known lamp has a tubular discharge vessel. A first and a second electrode arranged therein in mutual opposition, form means for maintaining an electric discharge in the discharge space. The discharge vessel has on an internal surface, a reflector layer which extends over the full length of the discharge vessel. The reflector layer leaves a portion of the circumference exposed so that a window is formed through which radiation can leave the discharge space. The reflector layer counteracts loss and undesirable dispersion of radiation and increases the intensity of radiation leaving the discharge space through the window. The reflector layer of the known lamp comprises aluminium oxide particles with an average size of 0.5-1.0 .mu.m.
Nevertheless, much radiation is lost in the known lamp owing to the fact that it is not reflected by the reflector layer. This is detrimental to the luminous efficacy of the lamp.